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Synergistic interactions between colistin and meropenem against extensively drug-resistant and pandrug-resistant Acinetobacter baumannii isolated from ICU patients
G Model ANTAGE-4532; No. of Pages 2
ARTICLE IN PRESS International Journal of Antimicrobial Agents xxx (2015) xxx–xxx
Contents lists available at ScienceDirect
International Journal of Antimicrobial Agents journal homepage: http://www.elsevier.com/locate/ijantimicag
Letter to the Editor Synergistic interactions between colistin and meropenem against extensively drug-resistant and pandrug-resistant Acinetobacter baumannii isolated from ICU patients Sir, Over the last years, Acinetobacter baumannii has been recognised as a serious human pathogen because of its capacity to cause outbreaks and to acquire multiple resistance mechanisms. The European Centre for Disease Prevention and Control (ECDC) reported a large proportion of invasive multidrug-resistant (MDR) A. baumannii isolates for 2013 and, more worryingly, the emergence of colistin-resistant isolates, which results in extensive drug resistance or pandrug resistance and compromises the efficacy of this last-resort antibacterial against A. baumannii. Combination therapy is a common strategy against MDR infections, but there are few in vitro data regarding the effectiveness of antibacterial combinations against colistin-resistant and pandrug-resistant (PDR) A. baumannii [1]. In this study, the in vitro interactions of five two-drug combinations, comprising colistin plus ampicillin/sulbactam (COL + SAM), colistin plus tigecycline (COL + TGC), colistin plus meropenem (COL + MEM), ampicillin/sulbactam plus meropenem (SAM + MEM) and ampicillin/sulbactam plus tigecycline (SAM + TGC), against three extensively drug-resistant (XDR) and two PDR A. baumannii isolates from five intensive care unit (ICU) patients at a tertiary hospital were studied. The minimum inhibitory concentration (MIC) of each drug was determined according to Clinical and Laboratory Standards Institute (CLSI) guidelines [2], and combinations were tested using the chequerboard technique at concentrations ranging from 1/8× MIC to 4× MIC in 96-well microplates. All combinations were tested in triplicate. Drug interactions were assessed both by the Loewe additivitybased fractional inhibitory concentration index (FICI) model and the Bliss independence-based response surface (BIRS) analysis in order to reduce analytical bias and to increase sensitivity in detecting significant pharmacodynamic interactions, as previously found [3]. For the FICI, microplates were visually inspected after 24 h of incubation and the FICI was calculated using the equation FIC = CA /MICA + CB /MICB , where CA and CB are the concentrations of drugs A and B in combination, and MICA and MICB are the MICs of drug A and drug B alone, respectively. Synergy, additivity or antagonism were concluded when the FICI was ≤0.5, >0.50 to <4 and ≥4, respectively. For BIRS analysis, percentage growth inhibition was determined spectrophotometrically at 630 nm as 100% − (OD − ODback )/OD0 − ODback ), where OD is the optical density of each well, ODback is the background optical density and OD0 is the optical density of the drug-free control well. Observed percentage growth inhibition (IOBS ) was compared with a theoretical
value (ITHE ), with the equation: ITHE = IA + IB − IA × IB , where IA and IB are the percentage growth inhibition of the drugs alone. Bliss synergy and antagonism were concluded when IOBS was significantly greater or smaller, respectively, than ITHE for all replicates, and Bliss independence was concluded if IOBS was not significantly different to ITHE [3]. In order to summarise all Bliss significant interactions, the difference I = IOBS − ITHE was calculated. All isolates were resistant to meropenem (MICs of 64–256 mg/L) and ampicillin/sulbactam (MICs of 128–256 mg/L). Three isolates were susceptible (MIC ≤ 0.5 mg/L) and two were resistant (MIC = 4 mg/L and 16 mg/L) to colistin. Tigecycline MICs ranged from 0.5 mg/L to 1 mg/L. All isolates were resistant to all other clinically relevant antibacterials. Synergy was found for COL + MEM for all five isolates with both drug interaction models. Notably, colistin activity was strongly enhanced in combination with meropenem, thus reaching clinically relevant concentrations. No other combination was found to be synergistic using the FICI analysis. However, synergy was found with the BIRS analysis for COL + SAM and COL + TGC combinations for all isolates. The SAM + TGC combination was also synergistic for three isolates, whilst SAM + MEM combination showed BIRS independence for all isolates (Table 1). Previous studies showed synergistic interactions of polymyxin plus imipenem or meropenem against A. baumannii isolates, but most isolates were polymyxin-susceptible. Shields et al. [4] found in vitro synergy of colistin plus meropenem against XDR A. baumannii isolated from solid-organ transplant recipients, and the clinical outcome of patients treated with this combination confirmed the in vitro results. Although efficient in vitro, tigecycline is not usually considered as a treatment option for A. baumannii infections because its clinical effectiveness is not established [US Food and Drug Administration (FDA), NDA 21-821/S-016, tigecycline prescribing information]. The emergence of XDR and PDR A. baumannii has resulted in increasing use of tigecycline against these infections, hence there is growing interest in the effectiveness of tigecycline against A. baumannii [5]. Whilst we found tigecycline-containing combinations additive by FICI analysis, BIRS analysis revealed synergy for COL + TGC and, to a lesser extent, for SAM + TGC. More experimental and clinical data are needed in order to evaluate the efficacy of tigecycline-containing antibacterial combinations. BIRS analysis showed that colistin may enhance ampicillin/sulbactam and tigecycline activity against MDR and PDR A. baumannii. Although FICI analysis is traditionally used for the evaluation of antibacterial interactions, it has some limitations, as described previously [3]. BIRS analysis may represent an alternative analysis method to assess antibacterial interactions as it appears to reveal subtle drug interactions. Finally, antibacterial combination therapy particularly with COL + MEM was synergistic in vitro and therefore merits further investigation in order to explore its clinical utility against these devastating infections.
http://dx.doi.org/10.1016/j.ijantimicag.2015.02.005 0924-8579/© 2015 Elsevier B.V. and the International Society of Chemotherapy. All rights reserved.
Please cite this article in press as: Vourli S, et al. Synergistic interactions between colistin and meropenem against extensively drug-resistant and pandrug-resistant Acinetobacter baumannii isolated from ICU patients. Int J Antimicrob Agents (2015), http://dx.doi.org/10.1016/j.ijantimicag.2015.02.005
G Model ANTAGE-4532; No. of Pages 2
ARTICLE IN PRESS Letter to the Editor / International Journal of Antimicrobial Agents xxx (2015) xxx–xxx
2
Table 1 Median (range) of minimum inhibitory concentrations (MICs) of drugs alone and in combination, fractional inhibitory concentration index (FICI) and percentage inhibition of drugs alone and in combination.
FICI analysis
BIRS analysis
MIC drug A MIC drug B MIC drug A comb. MIC drug B comb. FICI No. of synergistic interactions %IA %IB %IOBS %ITHE I (IOBS − ITHE ) No. of synergistic interactions
COL(A) + MEM(B)
COL(A) + SAM(B)
COL(A) + TGC(B)
0.5 (0.25–16) 128 (64–256) 0.125 (0.0625–1)
0.5 (0.25–16) 128 (128–256) 0.5 (0.125–2)
0.5 (0.25–16) 1 (0.5–1) 0.5 (0.25–8)
128 (64–256)
0.5 (0.25–1)
32 (16–64) 0.375 (0.2625–0.5) 5
0 (0–20) 0 (0–9) 100 (90–100) 0 (0–23) 99 (77–100) 5
1.5 (0.625–2) 0
0 (0–12) 0 (0–13) 90 (73–100) 2 (0–16) 77 (73–100) 5
SAM(A) + MEM(B)
SAM(A) + TGC(B)
128 (128–256) 128 (64–256) 128 (64–256)
128 (128–256) 1 (0.5–1) 128 (32–256)
2 (0.75–2) 0
5 (0–36) 8 (0–30) 69 (47–73) 13 (0–55) 47 (18–56) 5
64 (64–128) 1.5 (1–2) 0
0 (0–0) 0 (0–10) 0 (0–10) 0 (0–10) 0 (0–10) 0
0.5 (0.25–1) 2 (1.25–2) 0
8 (0–35) 39 (0–41) 61 (24–70) 45 (0–61) 19 (0–25) 3
COL, colistin; MEM, meropenem; SAM, ampicillin/sulbactam; TGC, tigecycline; %IA and %IB , percentage growth inhibition of the drugs alone; %IOBS , observed percentage growth inhibition; %ITHE , theoretical percentage growth inhibition; BIRS, Bliss independence-based response surface.
Funding None. Competing interests None declared. Ethical approval Not required. References [1] Zusman O, Avni T, Leibovici L, Adler A, Friberg L, Stergiopoulou T, et al. Systematic review and meta-analysis of in vitro synergy of polymyxins and carbapenems. Antimicrob Agents Chemother 2013;57:5104–11. [2] Clinical and Laboratory Standards Institute. Performance standards for antimicrobial susceptibility testing; twenty-third informational supplement. In: Document M100-S23. Wayne, PA: CLSI; 2013. [3] Meletiadis J, Verweij PE, TeDorsthorst DT, Meis JF, Mouton JW. Assessing in vitro combinations of antifungal drugs against yeasts and filamentous fungi: comparison of different drug interaction models. Med Mycol 2005;43:133–52. [4] Shields RK, Kwak EJ, Potoski BA, Doi Y, Adams-Haduch JM, Silviera FP, et al. High mortality rates among solid organ transplant recipients infected with extensively drug-resistant Acinetobacter baumannii: using in vitro antibiotic combination testing to identify the combination of a carbapenem and colistin as an effective treatment regimen. Diagn Microbiol Infect Dis 2011;70:246–52.
[5] Khawcharoenporn T, Pruetpongpun N, Tiamsak P, Rutchanawech S, Mundy LM, Apisarnthanarak A. Colistin-based treatment for extensively drug-resistant Acinetobacter baumannii pneumonia. Int J Antimicrob Agents 2014;43:378–82.
S. Vourli a,∗ F. Frantzeskaki b J. Meletiadis a L. Stournara b A. Armaganidis b L. Zerva a G. Dimopoulos b a Clinical Microbiology Laboratory, Attikon University Hospital, 1 Rimini Street, Haidari, 12462 Athens, Greece b Critical Care Medicine, Attikon University Hospital, 1 Rimini Street, Haidari, 12462 Athens, Greece ∗ Corresponding
author: Tel.: +30 210 583 1909 10; fax: +30 210 532 6421. E-mail addresses: [email protected], [email protected], [email protected] (S. Vourli). 13 January 2015 12 February 2015
Please cite this article in press as: Vourli S, et al. Synergistic interactions between colistin and meropenem against extensively drug-resistant and pandrug-resistant Acinetobacter baumannii isolated from ICU patients. Int J Antimicrob Agents (2015), http://dx.doi.org/10.1016/j.ijantimicag.2015.02.005
ARTICLE IN PRESS International Journal of Antimicrobial Agents xxx (2015) xxx–xxx
Contents lists available at ScienceDirect
International Journal of Antimicrobial Agents journal homepage: http://www.elsevier.com/locate/ijantimicag
Letter to the Editor Synergistic interactions between colistin and meropenem against extensively drug-resistant and pandrug-resistant Acinetobacter baumannii isolated from ICU patients Sir, Over the last years, Acinetobacter baumannii has been recognised as a serious human pathogen because of its capacity to cause outbreaks and to acquire multiple resistance mechanisms. The European Centre for Disease Prevention and Control (ECDC) reported a large proportion of invasive multidrug-resistant (MDR) A. baumannii isolates for 2013 and, more worryingly, the emergence of colistin-resistant isolates, which results in extensive drug resistance or pandrug resistance and compromises the efficacy of this last-resort antibacterial against A. baumannii. Combination therapy is a common strategy against MDR infections, but there are few in vitro data regarding the effectiveness of antibacterial combinations against colistin-resistant and pandrug-resistant (PDR) A. baumannii [1]. In this study, the in vitro interactions of five two-drug combinations, comprising colistin plus ampicillin/sulbactam (COL + SAM), colistin plus tigecycline (COL + TGC), colistin plus meropenem (COL + MEM), ampicillin/sulbactam plus meropenem (SAM + MEM) and ampicillin/sulbactam plus tigecycline (SAM + TGC), against three extensively drug-resistant (XDR) and two PDR A. baumannii isolates from five intensive care unit (ICU) patients at a tertiary hospital were studied. The minimum inhibitory concentration (MIC) of each drug was determined according to Clinical and Laboratory Standards Institute (CLSI) guidelines [2], and combinations were tested using the chequerboard technique at concentrations ranging from 1/8× MIC to 4× MIC in 96-well microplates. All combinations were tested in triplicate. Drug interactions were assessed both by the Loewe additivitybased fractional inhibitory concentration index (FICI) model and the Bliss independence-based response surface (BIRS) analysis in order to reduce analytical bias and to increase sensitivity in detecting significant pharmacodynamic interactions, as previously found [3]. For the FICI, microplates were visually inspected after 24 h of incubation and the FICI was calculated using the equation FIC = CA /MICA + CB /MICB , where CA and CB are the concentrations of drugs A and B in combination, and MICA and MICB are the MICs of drug A and drug B alone, respectively. Synergy, additivity or antagonism were concluded when the FICI was ≤0.5, >0.50 to <4 and ≥4, respectively. For BIRS analysis, percentage growth inhibition was determined spectrophotometrically at 630 nm as 100% − (OD − ODback )/OD0 − ODback ), where OD is the optical density of each well, ODback is the background optical density and OD0 is the optical density of the drug-free control well. Observed percentage growth inhibition (IOBS ) was compared with a theoretical
value (ITHE ), with the equation: ITHE = IA + IB − IA × IB , where IA and IB are the percentage growth inhibition of the drugs alone. Bliss synergy and antagonism were concluded when IOBS was significantly greater or smaller, respectively, than ITHE for all replicates, and Bliss independence was concluded if IOBS was not significantly different to ITHE [3]. In order to summarise all Bliss significant interactions, the difference I = IOBS − ITHE was calculated. All isolates were resistant to meropenem (MICs of 64–256 mg/L) and ampicillin/sulbactam (MICs of 128–256 mg/L). Three isolates were susceptible (MIC ≤ 0.5 mg/L) and two were resistant (MIC = 4 mg/L and 16 mg/L) to colistin. Tigecycline MICs ranged from 0.5 mg/L to 1 mg/L. All isolates were resistant to all other clinically relevant antibacterials. Synergy was found for COL + MEM for all five isolates with both drug interaction models. Notably, colistin activity was strongly enhanced in combination with meropenem, thus reaching clinically relevant concentrations. No other combination was found to be synergistic using the FICI analysis. However, synergy was found with the BIRS analysis for COL + SAM and COL + TGC combinations for all isolates. The SAM + TGC combination was also synergistic for three isolates, whilst SAM + MEM combination showed BIRS independence for all isolates (Table 1). Previous studies showed synergistic interactions of polymyxin plus imipenem or meropenem against A. baumannii isolates, but most isolates were polymyxin-susceptible. Shields et al. [4] found in vitro synergy of colistin plus meropenem against XDR A. baumannii isolated from solid-organ transplant recipients, and the clinical outcome of patients treated with this combination confirmed the in vitro results. Although efficient in vitro, tigecycline is not usually considered as a treatment option for A. baumannii infections because its clinical effectiveness is not established [US Food and Drug Administration (FDA), NDA 21-821/S-016, tigecycline prescribing information]. The emergence of XDR and PDR A. baumannii has resulted in increasing use of tigecycline against these infections, hence there is growing interest in the effectiveness of tigecycline against A. baumannii [5]. Whilst we found tigecycline-containing combinations additive by FICI analysis, BIRS analysis revealed synergy for COL + TGC and, to a lesser extent, for SAM + TGC. More experimental and clinical data are needed in order to evaluate the efficacy of tigecycline-containing antibacterial combinations. BIRS analysis showed that colistin may enhance ampicillin/sulbactam and tigecycline activity against MDR and PDR A. baumannii. Although FICI analysis is traditionally used for the evaluation of antibacterial interactions, it has some limitations, as described previously [3]. BIRS analysis may represent an alternative analysis method to assess antibacterial interactions as it appears to reveal subtle drug interactions. Finally, antibacterial combination therapy particularly with COL + MEM was synergistic in vitro and therefore merits further investigation in order to explore its clinical utility against these devastating infections.
http://dx.doi.org/10.1016/j.ijantimicag.2015.02.005 0924-8579/© 2015 Elsevier B.V. and the International Society of Chemotherapy. All rights reserved.
Please cite this article in press as: Vourli S, et al. Synergistic interactions between colistin and meropenem against extensively drug-resistant and pandrug-resistant Acinetobacter baumannii isolated from ICU patients. Int J Antimicrob Agents (2015), http://dx.doi.org/10.1016/j.ijantimicag.2015.02.005
G Model ANTAGE-4532; No. of Pages 2
ARTICLE IN PRESS Letter to the Editor / International Journal of Antimicrobial Agents xxx (2015) xxx–xxx
2
Table 1 Median (range) of minimum inhibitory concentrations (MICs) of drugs alone and in combination, fractional inhibitory concentration index (FICI) and percentage inhibition of drugs alone and in combination.
FICI analysis
BIRS analysis
MIC drug A MIC drug B MIC drug A comb. MIC drug B comb. FICI No. of synergistic interactions %IA %IB %IOBS %ITHE I (IOBS − ITHE ) No. of synergistic interactions
COL(A) + MEM(B)
COL(A) + SAM(B)
COL(A) + TGC(B)
0.5 (0.25–16) 128 (64–256) 0.125 (0.0625–1)
0.5 (0.25–16) 128 (128–256) 0.5 (0.125–2)
0.5 (0.25–16) 1 (0.5–1) 0.5 (0.25–8)
128 (64–256)
0.5 (0.25–1)
32 (16–64) 0.375 (0.2625–0.5) 5
0 (0–20) 0 (0–9) 100 (90–100) 0 (0–23) 99 (77–100) 5
1.5 (0.625–2) 0
0 (0–12) 0 (0–13) 90 (73–100) 2 (0–16) 77 (73–100) 5
SAM(A) + MEM(B)
SAM(A) + TGC(B)
128 (128–256) 128 (64–256) 128 (64–256)
128 (128–256) 1 (0.5–1) 128 (32–256)
2 (0.75–2) 0
5 (0–36) 8 (0–30) 69 (47–73) 13 (0–55) 47 (18–56) 5
64 (64–128) 1.5 (1–2) 0
0 (0–0) 0 (0–10) 0 (0–10) 0 (0–10) 0 (0–10) 0
0.5 (0.25–1) 2 (1.25–2) 0
8 (0–35) 39 (0–41) 61 (24–70) 45 (0–61) 19 (0–25) 3
COL, colistin; MEM, meropenem; SAM, ampicillin/sulbactam; TGC, tigecycline; %IA and %IB , percentage growth inhibition of the drugs alone; %IOBS , observed percentage growth inhibition; %ITHE , theoretical percentage growth inhibition; BIRS, Bliss independence-based response surface.
Funding None. Competing interests None declared. Ethical approval Not required. References [1] Zusman O, Avni T, Leibovici L, Adler A, Friberg L, Stergiopoulou T, et al. Systematic review and meta-analysis of in vitro synergy of polymyxins and carbapenems. Antimicrob Agents Chemother 2013;57:5104–11. [2] Clinical and Laboratory Standards Institute. Performance standards for antimicrobial susceptibility testing; twenty-third informational supplement. In: Document M100-S23. Wayne, PA: CLSI; 2013. [3] Meletiadis J, Verweij PE, TeDorsthorst DT, Meis JF, Mouton JW. Assessing in vitro combinations of antifungal drugs against yeasts and filamentous fungi: comparison of different drug interaction models. Med Mycol 2005;43:133–52. [4] Shields RK, Kwak EJ, Potoski BA, Doi Y, Adams-Haduch JM, Silviera FP, et al. High mortality rates among solid organ transplant recipients infected with extensively drug-resistant Acinetobacter baumannii: using in vitro antibiotic combination testing to identify the combination of a carbapenem and colistin as an effective treatment regimen. Diagn Microbiol Infect Dis 2011;70:246–52.
[5] Khawcharoenporn T, Pruetpongpun N, Tiamsak P, Rutchanawech S, Mundy LM, Apisarnthanarak A. Colistin-based treatment for extensively drug-resistant Acinetobacter baumannii pneumonia. Int J Antimicrob Agents 2014;43:378–82.
S. Vourli a,∗ F. Frantzeskaki b J. Meletiadis a L. Stournara b A. Armaganidis b L. Zerva a G. Dimopoulos b a Clinical Microbiology Laboratory, Attikon University Hospital, 1 Rimini Street, Haidari, 12462 Athens, Greece b Critical Care Medicine, Attikon University Hospital, 1 Rimini Street, Haidari, 12462 Athens, Greece ∗ Corresponding
author: Tel.: +30 210 583 1909 10; fax: +30 210 532 6421. E-mail addresses: [email protected], [email protected], [email protected] (S. Vourli). 13 January 2015 12 February 2015
Please cite this article in press as: Vourli S, et al. Synergistic interactions between colistin and meropenem against extensively drug-resistant and pandrug-resistant Acinetobacter baumannii isolated from ICU patients. Int J Antimicrob Agents (2015), http://dx.doi.org/10.1016/j.ijantimicag.2015.02.005